Problem Statement

Merge two sorted linked lists and return it as a sorted list. The list should be made by splicing together the nodes of the first two lists.

Example 1:

Input: l1 = [1,2,4], l2 = [1,3,4]
Output: [1,1,2,3,4,4]

Example 2:

Input: l1 = [], l2 = []
Output: []

Example 3:

Input: l1 = [], l2 = [0]
Output: [0]

Constraints:

• The number of nodes in both lists is in the range [0, 50].
• 100 <= Node.val <= 100
• Both l1 and l2 are sorted in non-decreasing order.

Problem Link

Merge Two Sorted Lists - LeetCode

Code

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        
        if(!l1)
            return l2;
        
        if(!l2)
            return l1;
        
        ListNode dummy(0);
        ListNode *head = &dummy;
        
        while(l1&&l2)
        {
            if(l1->val<=l2->val)
            {
                head->next = l1;
                l1 = l1->next;
            }
            else
            {
                head->next = l2;
                l2 = l2->next;
            }
            
            head = head->next;
            
            
        }
        
        while(l1)
        {
            head->next = l1;
                l1 = l1->next;
            head = head->next;
        }
        
        while(l2)
        {
            head->next = l2;
                l2 = l2->next;
            head = head->next;
        }
        return dummy.next;
        
        
    }
};